Solenoids



Nov. 4, 1969 J. A. KNOWLES SOLENOIDS Filed March 28, 1968 o m w mw rm En JR W Wm I M J United States Patent 3 Claims ABSTRACT OF THE DISCLOSURE In a solenoid of the kind comprising a casing, an armature axially movable within the casing, and pull in and hold in windings within the casing, the armature is in two parts. The first inner part of the armature is urged outwardly of the casing by a first spring, and the second outer part of the armature is co-axial with the first part, and is urged inwardly of the casing by a second spring. The first spring is stronger than the second spring, and the arrangement is such that when the windings are not energised the first part engages the second part under the action of the first spring. and the second part is thereby moved outwardly against the action of the second spring.

This invention relates to solenoids of the kind comprising a casing, an armature axially movable within the easing, and pull in and hold in windings within the casing.

According to the invention, in a solenoid of the kind specified the armature is in two parts, a first, inner part which is urged outwardly of the casing by a first spring and a second, outer part coaxial with the first part and urged inwardly of the casing by a second spring, said first spring being stronger than said second spring and the arrangement being such that when said windings are not energised said first part engages said second part under the action of said first spring, and said second part is moved outwardly against the action of said second spring.

In the accompanying drawings FIGURE 1 is a sectional view of a solenoid according to one example of the invention, and FIGURE 2 is a fragmentary sectional view of a modification of the solenoid shown in FIGURE 1.

Referring to the drawings, the solenoid includes a hollow cylindrical casing 11, one end of which is closed by an end core 12 having secured thereto the body of a normally closed switch 13. Slidable axially within the casing 11 is a steel first part 14 of an armature which is urged outwardly of the casing 11 by a first spring 16 acting between the part 14 of the armature and the closed end of the casing. Housed within the casing 11 is a pair of coils 18 constituting respectively the hold in and pull in windings of the solenoid, the pull in winding being connected in use to a DC. supply through the switch 13.

At its end remote from the switch 13 the casing 11 includes a bearing block 19 formed from non-magnetic material, having extending therethrough a stepped bore 21. Slidable axially in the bore 21 of the bearing block 19 is a steel second part 15 of the armature, coaxial with the part 14 of the armature. The part 15 of the armature projects from the bearing block 19 at its end remote from the main part of the casing 11 and is urged towards the part 14 of the armature by a second spring 17 acting between the annular shoulder 22 of the stepped bore 21 in the bearing block 19 and a flange 23 on the part 15 of the armature. The spring 16 is stronger than the spring 17 so that when the windings 18 are not energised the spring 16 urges the part 14 of the armature outwardly into abutment with the part 15 of the armature which is moved against the action of the spring 17.

When it is desired to operate the solenoid, the pull in 3,477,048 Patented Nov. 4, 1969 "ice winding and the hold in winding are energised simu1taneously and the part 14 of the armature is drawn into the casing 11 against the action of the spring 16, the part 15 of the armature being moved with the part 14 by the action of the spring 17.

When the part 14 of the armature has moved a predetermined distance towards the switch 13 closing said one end of the casing 11, the part 14 of the armature engages a plunger 24 associated with the switch 13 and further movement of the part 14 of the armature towards the switch 13 opens the switch 13 to de-energise the pull in winding, the part 14 of the armature being maintained in its inner position by the hold in winding which remains energised.

It is important when a road vehicle is being driven, with its internal combustion operating at a high speed, that the driver does not select a lower gear which would cause the engine to operate at an even higher speed resulting in damage to the engine of the vehicle.

In one application of the invention the solenoid is used to control a latch mechanism associated with a road vehicle gearbox.

The hold in and pull in windings 18 of the solenoid are energised through a switch which is sensitive to engine speed and which is closed only when the engine speed is below a predetermined level and the part 15 of the armature constitutes a latch mechanism in the gearbox of the vehicle which is operable to prevent the selection of a lower gear.

When the vehicle is being driven with its engine operating above said predetermined speed the speed sensitive switch is open and the armature 14, 15 is in its outer position so that the latch mechanism in the gearbox is locked so preventing the driver of the vehicle selecting a lower gear. However, when the engine falls to a speed below the predetermined speed the speed sensitive switch will close and the hold in and pull in windings 18 will be energised and the armature 14, 15 will be moved to its inner position to free gearbox to allow the selection of a lower gear.

Should the driver of the vehicle apply pressure to the gear selector lever to select a lower gear as the engine speed falls, then the part 15 will be subject to pressure and will become trapped against subsequent inward movement. Thus, when the speed sensitive switch closes the pull in and hole in windings 18 will be energised and the part 14 of the armature will be moved inwardly and will open the switch 13 to de-energise the pull in winding. However, the part 15 of the armature will not move inwardly under the action of the spring 17 to free the gearbox until the pressure on the gear selector lever is released.

It will be appreciated that if the armature were of one part construction, then if the pull in and hold in windings 18 were energised while the armature was trapped against inward movement, then the pull in winding would remain energised and would probably be burnt out.

The bearing block 19 is formed from non-magnetic material in order to reduce the magnetic attraction between the parts 14, 15 of the armature in use.

In the modification shown in FIGURE 2 a non-magnetic spacer 25 is secured to either the part 14 or the part 15 of the armature, and serves to maintain a predetermined air gap between the parts 14, 15, again to reduce the magnetic attraction between the two parts.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. A solenoid of the kind specified wherein the armature is in two parts, a first, inner part which is urged outwardly of the casing by a first spring and a second, outer part coaxial with the first part and urged inwardly of the casing by a second spring, said first spring being stronger than said second spring and the arrangement being such that when said windings are not energised said first part engages said second part under the action of said first spring, and said second part is moved outwardly against the action of said second spring.

2. A solenoid as claimed in claim 1 wherein both parts of the armature are formed from ferrous material and means are provided for reducing the magnetic attraction between said parts in use.

3. A solenoid as claimed in claim 2 wherein said means includes a non-magnetic spacer secured to one of said parts and engageable with the other of said part to maintain a predetermined air gap between the parts, when the parts are moved towards one another.

. 4 1 References Cited UNITED'STATES PATENTS 2,935,663 5/1960 Pollak 335-264 3,158,144 11/1964 Walker "123-102 LEE T. HIX, Primary Examiner I. HARNISI-L Assistant Examiner US. Cl. X.R. 

